Method for magnetron strap mounting



July 29, 1958 E. c. oKREs'S METHOD FOR MAGNETRON STRAP MOUNTING 2 Sheets-Sheet 1 Filed March 15, 1955 all y 9, 1958 E. c. OKRESS 2,845,576

' METHOD FOR MAGNETRON STRAP MOUNTING Filed March 15, 1955 2 Sheets-Sheet 2 United States Patent METHOD FOR MAGNETRON STRAP MOUNTING Ernest C. Okress, Montclair, N. J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application March 15, 1955, Serial No. 494,583

12 Claims. (Cl. 315-39.69)

This invention concerns strapped magnetrons and the mounting of straps on the anodes of strapped magnetrons.

A multicavity magnetron comprises an anode structure with a plurality of segments adjacent a cathode. The dimensions of the anode structure determine the fre quency of oscillation of the electromagnetic field in the magnetron. The magnetron, in normal operation, oscillates in a predetermined mode in order to generate a predetermined frequency. The stability and efficiency of the magnetron are considerably decreased when spurious modes of oscillation occur.

Conductors are attached to the ends of the anode segments in one method of obtaining higher efliciency and better mode stability. The technique of attaching conductors to the anode segments is known as strapping. Single ring strapping is the utilization of one circular ring at each end of the anode body to connect alternate anode segments. Double ring strapping is the utilization of two circular ring conductors at each end of the anode body to connect alternate anode segments. Better mode stability ensues from double ring strapping than from single ring strapping.

For higher frequency production, anodes are made smaller and are provided with a larger number of cavities (between the segments of the anode). The small dimensions and small clearances imposed by smaller anodes and more cavities make strapping difficult. Since high radio frequency electric field intensity between straps occurs at very high powers, good electrical contact to the segments is even more important than at much lower power levels.

Anode strapping methods of the prior art entail expensive machining operations and skilled handwork in aligning and brazing the straps to the anode body.

There are many disadvantages inherent in prior art methods of brazing straps to magnetron anode bodies. The brazing wire is mounted on the strap after pretuning the magnetron with the strap in place; this avoids interference with electrostatic action of the straps during pretuning. If the straps are brazed before the anode is pretuned, mechanical distortion must be inflicted upon the straps in order to obtain the desired frequency. Mechanical strap distortion produces undesirable effects on electropolished straps and in the spacing between straps and between straps and anode.

The prior art use of a brazing wire form after pretuning results in electropolished strap scratches and anode surface scratches due to mounting of the form. The thermal contact between the brazing wire form and the strap and anode body varies and is usually poor; this permits unmelted portions of the brazing wire to remain on the strap and/ or anode body. Since the brazing wire is unhampered is moving, twisting or curling, during brazing, it frequently melts in undesirable areas of the strap and anode body.

In the prior art, to conform the brazing wires to the shape of the strap legs a fixture is necessary to form the brazing wires.

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The principal object of this invention is the provision of a method of mounting magnetron straps.

An object of this invention is the provision of a method of mounting magnetron straps before or during pretuning.

An object of this invention is the provision of a method of mounting magnetron straps on anode bodies of very small dimensions.

An object of this invention is the provision of a method of mounting magnetron straps which is exact and inexpensive.

An object of this invention is the provision of a method of mounting magnetron straps which prevents mechanical strap distortion.

Another object of this invention. is the provision of a method of mounting magnetron straps which avoids the use of brazing wire preforming.

A further object of this invention is the provision of a method of mounting magnetron straps which avoids the necessity for using a fixture.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is' a plan view of a magnetron anode body, well known in the art, with its segments unstrapped;

Fig. 2 is a sectional view of the magnetron anode body of Fig. 1;

Fig. 3 is an isometric cross-sectional view of the magnetron anode body of Figs. 1 and 2, strapped; and

Fig. 4 is an enlarged sectional view of a portion of a segment of the magnetron anode body, strapped by the method of the present invention.

The symmetrical magnetron anode body 1 shown in Figs. 1-4 is produced from suitable electrically conductive material, such as oxygen free high conductivity copper. The anode segments 2 provide a' series of cavity resonators 3 therebetween. An annular strap slot 4 is formed across the free end portion of each anode 1, leaving inner ridges 5 on the anode segments 2.

There is provided straps 6, 7, 8, and 9. Each of the straps has arcuately spaced base portions whereby each of the straps interconnect alternate anode segments 2. Assuming the segments '2 to be numbered consecutively, the top inner strap *8 contacts and interconnects the even numbered anode segments 2, while the top outer strap 9 contacts and interconnects the odd numbered anode segments 2. In a complementary fashion,- the lower inner strap 7 contacts and interconnects the odd numbered anode segments 2, while the lower outer strap 6 contacts and interconnects the even numbered anode segments 2.

The arrangement of strapping shownin Fig. 3 and described above is well known in the art.

The straps of high power magnetrons are secured on the anode segments by brazing in order to attain the following features. Brazing insures adequate electrical contact between the strap and the anode segment; this prevents sparking at the contact joint which may ensue from circulating currents in the strap. Brazing provides adequate thermal contact between the strap and the anode segment; this keeps the strap as coolas possible. by providing maximum heat conduction across the contact joint. Brazing imposes adequate mechanical restraint to prevent relative movement between the strap and the-anode segment; this maintains a constant strap break width and a tight contact between the strap and anode segment. The enlarged portion of the anode segment shown in Fig. 4 shows the upper strap slot of one anode segment. Only strap 8 contacts and is secured to the segment shown. I The bases of the annular slots 4 are recessed to form 3 coaxial annular grooves that are uniformly interrupted arcuately at the cavity resonators 3. The width and depth of the grooves 10 are substantially equal to the width of the straps. Additionally the base portions of the straps are formed with grooves 12.

Pieces of brazing wire 13 are utilized in lengths -approximately equal to the width of the anode segments. One piece of brazing wire is fitted into each groove 12 in each base portion of each strap. After each piece of brazing wire 13 is inserted in a strap groove, the sides of the corresponding base portion are pinched together somewhat, as by a pair of pliers, to secure the pieces of brazing wire 13 in the straps. The brazing Wire, when fused, fills only the joints between the base portions of the straps and the segment surfaces which form the grooves 10. The brazing wire thus does not adversely affect the electro-polished surfaces of the straps, since it does not flow over them, when fused. Also, the strap surfaces are not scratched by the brazing wire during the mounting operation, and the brazing wire may be mounted before pretuning the anode.

After the brazing wire is secured in the strap grooves 12, the strap is seated in the slot grooves 10. The outer edges of the grooves 10 adjacent the strap are lightly peened at 11 to mechanically secure the strap in the slot grooves 10. This peening is preferably done in a low potential region such as the side of the strap 8 of Fig. 4 facing the inner ridge 5. It is preferable not to peen the strap on its side facing the strap 9 in order to avoid detrimental etfects due to surface scratching by the peening tool. The peened metal 11 of the segment supports the strap during the brazing operation, which follows. The brazing process secures the strap in the grooves 10 in the anode segments. A small amount of the braze appears at the edges of the joints after melting.

The method of strap mounting of the present invention is not limited to the strap-ping arrangement shown in Figs. 3 and 4, but may be applied to many strapping arrangements as well as to many types of symmetric cavity magnetrons.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. An improved method of strapping a multicavity type magnetron anode body with a pair of anode straps each of which has base portions for contacting alternate anode arms, said method comprising the steps of slotting the anode arms to form at least one annular slot that is uniformly interrupted arcuately by the anode cavities, grooving the bases of the slots in the anode arms to form two coaxial annular grooves that are uniformly inter: rupted arcuately by the anode cavities, the width of the grooves being substantially the same as the width of the anode straps, grooving the base portions of the straps, inserting lengths of wire-like conductive material of lower fusing temperature than the anode body and the anode straps in the base portions of the straps, each said conductive material having a length approximately equal to the Width of the anode segment which it abuts, and aligned with that anode segment, pinching the base portions of the straps to retain the wire-like material in the grooves of the base portions, assembling the anode body and the anode straps whereby the base portions of one of the anode straps contacts the bases of the grooves in alternate arms in the anode body and the base portions of the other anode strap contacts the bases of grooves in the remainder of the arms in the anode body, and fusing the wire-like material while the straps are held in said arms.

2 An improved method of strapping a multicavity type magnetron anode body with a pair of anode straps each of which has base portions for contacting alternate anode arms, said method comprising the steps of slotting the anode arms to form at least one annular slot that is uniformly interrupted arcuately by the anode cavities, grooving the bases of the slots in the anode arms to form two coaxial annular grooves that are uniformly interrupted arcuately by the anode cavities, the width and depth of the grooves being substantially the same as the width of the anode straps, grooving the base portions of the straps, inserting lengths of wire-like conductive material of lower fusing temperature than the anode body and the anode straps in the base portions of the straps, each said conductive material having a length approximately equal to the width of the anode segment which it abuts, and aligned with that anode segment, pinching the base portions of the straps to retain the wire-like material in the groove base portions, assembling the anode body and the anode straps whereby base portions of one of the anode straps contacts the bases of the grooves in alternate arms in the anode body and the base portions of the other anode straps contacts the bases of grooves in the remainder of the arms in the anode body, peening edge portions of the grooves to retain the anode body and anode straps in assembled relationship, and fusing the wire-like material while the straps are mechanically held in position by the peening.

3. An improved method of securing a metallic straplike member to one of the spaced apart arms of another metallic member which it bridges comprising forming a groove in the base of the strap-like member, inserting a length of metallic material of lower fusing temperature than the strap-like member and the other member in the groove in the base of the strap-like member and mechanically securing it therein, said length of material having a length approximately equal to the width of the arm across which it is to extend, forming a groove in an arm of the other member of substantially the same width as the corresponding width of the strap-like member, assembling the strap-like member in said groove of said other member with said length of material aligned with one of said arms, whereby the strap-like member is supported in the groove in the other member, and fusing the material while said member is held in said groove.

4. An improved method of strapping a multicavity type magnetron anode body having a plurality of anode arms extending radially of a common axis to form anode cavities between them and with two concentric annular slots that are interrupted arcuately by the anode cavities, with a pair of anode straps each of which has base portions extending edgewise therefrom for contacting the bases of the slots in alternate anode arms, said method comprising the steps of grooving the bases of the slots in the anode arms to form two coaxial annular grooves that are interrupted arcuately by the anode cavities, the widths of the grooves in a direction radial to said axis being substantially the same as the corresponding widths of the anode straps, grooving that edge of the base portions of the straps which fit the bases of the grooves, inserting lengths of conductive material of lower fusing temperature than the anode body and the anode straps in the grooves in the base portions of the straps solely where they engage with an anode arm, which lengths do not materially exceed the width of an anode arm, assembling the anode body and the anode straps with theextending base portions of one of the anode straps contacting the bases of the grooves in alternate arms in the anode body and with the base portions of the other anode strap contacting the bases of grooves in the remainder of the arms in the anode body, and fusing the material in said base portions while the straps are confined in said grooves in said arms.

5. The method as set forth in claim 4, and mechanically confining the straps in said grooves before said fusing by peening an edge portion of each groove against the strap in that groove.

6. In a multi-cavity magnetron anode of the type having a plurality of spaced anode segments with transverse strap slots and similarly exte-iding but narrower grooves in the bottom of the slots, and a metallic strap extending across said segments in said slots and received and held edgewise in the grooves in alternate segments, that improvement therein which comprises said strap having, in

the edge portion thereof within each groove, an open channel extending along that edge, and a brazing material within each such channel solely in the portions thereof within a groove and mechanically and electrically uniting the strap to said alternate segments, said segments and strap being substantially free of said brazing material exteriorly of said grooves.

7. The anode as set forth in claim 6, wherein the bottom of the slot of a segment, along that edge of a groove nearest the free end of that segment, is mechanically upset against the strap in that nearest groove.

8. A multi-cavity magnetron anode comprising an anode body having a plurality of anode segments, each of said anode segments having a strap slot and a groove in the bottom of the strap slot, a metallic anode strap disposed in said slots, extending between said segments, and having, at spaced intervals along it, tongues, extending edgewise therefrom into the grooves of alternate segments for support thereby, the edges of said tongues which rest on the bottoms of the strap slots in alternate segments of said anode body having channels running in directions lengthwise of such edges, and electrically conducting brazing material in each of said channels and electrically and mechanically uniting said tongues to the bottoms of said grooves of said segments, said segments and strap being substantially free of said brazing material exteriorly of said grooves.

9. A multi-cavity magnetron anode comprising an anode body with a plurality of anode segments, with said segments having transversely crossing strap slots and similarly crossing but narrower grooves in the bottoms of said slots, a metallic strap extending from segment in said slots and having spaced edge portions received in and fitting the grooves of alternate grooves, with the straps out of electrical contact with the other alternate segments, each of said edge portions having a channel in that part of a wall thereof which is received in a segment groove, and a strip of brazing material solely in those parts of said channels which are closed by said grooves and mechanically and electrically uniting said straps to said alternate anode segments, said segments and strap being substantially free of said brazing material exteriorly of said grooves.

10. A multi-cavity magnetron anode comprising an anode body with a plurality of anode segments arranged in a circular row with each segment radial to said row and all having in corresponding faces thereof a transversely crossing strap slot, each segment also having a pair of similarly crossing but narrower grooves in the bottom wall of the slot and spaced apart in a direction radially of said row, a pair of metallic rings disposed in all of said slots and concentric with each other and with the row of segments, one strap having edgewise portions received in and fitting the narrower grooves nearest the free ends of alternate segments but clearing the other alternate segments, the other strap in the same slot being received in and fitting the other narrower grooves in the other alternate segments but clearing the first mentioned alternate segments, each strap having a channel in each edge portion thereof within a groove, and a brazing material solely within that portion of each channel within a groove and mechanically and electrically uniting each of said straps to its said alternate segments, said segments and straps being substantially free of said brazing material outside of said grooves.

11. The method as set forth in claim 3, wherein said mechanical securing of said length of material is by pinching closed slightly the open face of said groove after said length of material is inserted therein.

12. The method as set forth in claim 4, and pinching slightly in a closing direction the material of the straps at open faces of the grooves after the lengths of material are inserted in those grooves.

References Cited in the file of this patent UNITED STATES PATENTS 2,440,298 Ronay et a1 Apr. 27, 1948 2,448,907 Ost Sept. 7, 1948 2,535,713 Wooten Dec. 26, 1950 2,550,614 Spencer Apr. 24, 1951 2,559,604 Donal et al July 10, 1951 2,645,843 Nordsieck July 21, 1953 2,710,364 Gutton et a1 June 7, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,845,576 July 29, 1958 Ernest C. Okress It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 19, after "using a fixture." insert the following paragraph:

-- A further object of this invention is to provide an improved strapped magnetron anode. "a

Signed and sealed this 17th day of February 1959a SEAL) ttest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

